Homeostasis Lecture Notes

Introduction

• Homeostasis: State of balance within body systems.
• Importance of balance in physiological processes.
• Key methods of maintaining homeostasis: Negative feedback and positive feedback mechanisms.

Negative Feedback Mechanism

Example 1: Blood Glucose Regulation

• Stimulus: Change in blood glucose levels (too high or too low).
• High Glucose Levels:
  • Detected by Glut receptors on pancreatic alpha cells.
  • Pancreas (Control center) produces Insulin.
  • Insulin facilitates glucose uptake by body cells, lowering blood glucose levels.
• Low Glucose Levels:
  • Detected by Glut receptors.
  • Pancreas produces Glucagon.
  • Glucagon causes the liver to release glucose into the bloodstream, increasing blood glucose levels.
• Process: Stimulus → Glut receptors (Receptor) → Pancreas (Control Center) → Insulin/Glucagon (Efferent Signal) → Cells/Liver (Effector) → Response.

Example 2: Body Temperature Regulation

• Cold Temperature:
  • Detected by Thermoreceptors in the skin.
  • Hypothalamus (Control center) responds to efferent signals.
  • Responses:
    • Vasoconstriction of blood vessels to reduce heat loss.
    • Shivering to increase heat production.
    • Inhibiting sweat production to prevent cooling.
• Hot Temperature:
  • Detected by thermoreceptors.
  • Hypothalamus sends signals to:
    • Vasodilate blood vessels to increase heat loss.
    • Increase sweat production for evaporative cooling.
    • Inhibit shivering to reduce heat production.
• Process: Stimulus → Thermoreceptors (Receptor) → CNS/Hypothalamus (Control Center) → Blood vessels/Muscles (Effector) → Response.

Positive Feedback Mechanism

Example 1: Birthing Process

• Stimulus: Cervical stretch during childbirth.
• Activation of stretch receptors.
• Hypothalamus and posterior pituitary release Oxytocin.
• Oxytocin causes uterine contractions, further stretching cervix.
• Cycle: Stimulus → Stretch Receptors (Receptor) → Hypothalamus (Control Center) → Oxytocin (Efferent Signal) → Uterus (Effector) → Increased Contractions.

Example 2: Lactation

• Stimulus: Suckling at the breast.
• Mechanoreceptors send signals to hypothalamus and anterior/posterior pituitary.
• Prolactin (Anterior Pituitary) stimulates milk production.
• Oxytocin (Posterior Pituitary) causes milk ejection.
• Cycle: Stimulus → Mechanoreceptors (Receptor) → Hypothalamus (Control Center) → Prolactin/Oxytocin (Efferent Signal) → Mammary glands (Effector) → Milk production/ejection.

Example 3: Blood Clotting

• Stimulus: Injury to a blood vessel.
• Platelets adhere to the injury site, releasing chemicals to recruit more platelets.
• Formation of a platelet plug to seal the injury.
• Cycle: Stimulus → Platelets (Receptor & Effector) → Chemical Signals (Efferent Signal) → More Platelets (Effector) → Amplified Response.

Conclusion

• Negative feedback maintains balance by counteracting changes, while positive feedback amplifies responses for specific physiological processes.
• Understanding these mechanisms is crucial for comprehending physiological homeostasis and related pathologies.